Field of the Invention
The present invention relates to a liquid discharge head and a liquid discharge apparatus for discharging desired liquid by generation of a bubble induced by action of thermal energy on the liquid, and more particularly to the configuration of a substrate on which is formed a thermal energy generating element for generating thermal energy.
The present invention is applicable to an apparatus such as a printer for recording on various recording media such as paper, yarn, fiber, cloth, metal, plastics, glass, timber or ceramics, a copying apparatus, a facsimile apparatus provided with a communication system, or a word processor equipped with a printer unit, or to an industrial recording apparatus combined with various processing apparatuses.
In the present invention, the term "recording" means not only providing the recording medium with a meaningful image such as a character or graphics but also with a meaningless image such as a pattern.
There is already known the so-called bubble jet recording method, namely an ink jet recording method of providing ink with an energy such as heat to cause a state change involving an abrupt volume change in the ink, discharging ink from the discharge opening by an action force based on such state change and depositing the ink onto a recording medium to form an image. The recording apparatus employing such bubble jet recording method is generally provided, as disclosed in U.S. Pat. No. 4,723,129, with a discharge opening for discharging ink, an ink path communicating with the discharge opening and an electrothermal converting member provided in the ink path and serving as energy generating means for generating energy for discharging the ink.
Such recording method has various advantages, such as recording an image of high quality at a high speed with a low noise level, and recording an image of a high resolution or even a color image with a compact apparatus since, in the head executing such recording method, the ink discharge openings can be arranged at a high density. For this reason, the bubble jet recording method is recently employed in various office equipment such as printers, copying machines, facsimile machines, etc., and even in industrial systems such as fabric dyeing apparatuses.
With the spreading of the bubble jet technology into various fields, various demands are arising as explained in the following.
For example, in order to satisfy a demand for improving the energy efficiency, there is conceived optimization of the heat generating member, such as adjustment of the thickness of the protective film for the heat generating member. This method is effective in improving the efficiency of propagation of the generated heat to the liquid.
Also for obtaining an image of high quality, there is proposed a driving method for liquid discharge capable of realizing a faster ink discharging speed and satisfactory ink discharge based on stable bubble generation, and, for achieving high-speed recording, there is proposed an improved shape of the liquid path for realizing the liquid discharge head with a faster refilling speed of the liquid into the liquid path.
The present invention is to improve the fundamental discharge characteristics of the basically conventional method of discharging liquid by forming a bubble, particularly a bubble based on film boiling, in the liquid path, to a level that cannot be anticipated before.
The present inventors have made intensive investigations in order to provide a novel liquid droplet discharging method utilizing the conventionally unavailable bubble and a head utilizing such method. In these investigations, there have been executed a first technical analysis on the function of the movable member in the liquid path, analyzing the principle of the mechanism of the movable member in the liquid path, a second technical analysis on the principle of liquid droplet discharge by the bubble, and a third technical analysis on the bubble forming area of the heat generating member for bubble formation, and, through these analyses, there has been established a completely novel technology of positively controlling the bubble by positioning the fulcrum and the free end of the movable member in such a manner that the free end is provided at the side of the discharge opening or at the downstream side and by positioning the movable member so as to be opposed to the heat generating member or the bubble generating area.
Then, in consideration of the effect of the energy of the bubble itself on the discharge amount, there is obtained knowledge that the growing component in the downstream side of the bubble is the largest factor capable of drastically improving the discharge characteristics. More specifically, it has been found that the efficient conversion of the growing component in the downstream side of the bubble toward the discharging direction leads to an improvement in the discharge efficiency and discharge speed.
It has further been found that structural consideration is desirable on the movable member or the liquid path relating to the heat generating area serving to form the bubble, for example relating to the bubble growth in the downstream side with respect to the central line passing through the areal center of the electrothermal converting member in the liquid flowing direction, or in the downstream side of the bubble with respect to the areal center of the area contributing to the bubble generation.
It has further been found that the refilling speed can be significantly improved by giving consideration to the arrangement of the movable member and the structure of the liquid supply path.